Extreme High Voltage: TinselKoil 4 — MOT DC Tesla Coil w/ Blown Spark Gap Quenching

Here’s my “current” project: A small Tesla coil, with primary power from a Microwave Oven Transformer and a high-voltage Full Wave Bridge rectifier. I used a simple 2-element “blown” primary spark gap.

In this video I show the importance of proper quenching of the primary spark gap in order to make the quick transition needed to stimulate the extreme HV ringing of the secondary.

I know the MOT is not the ideal supply for a Tesla coil, at only 2 kV and too much current, but using it as a DC source works fairly well as you can see. Some current limiting might be a good thing to employ. Next I will be trying a small standard Neon Sign Transformer of 6500 Volts 30 mA, which might work even better.
I demonstrate the effect of the compressed air blast, showing that without the quenching the MOT supplies enough current to “arc” over the gap without making a fast turn-off. Adding the air blast at the same gap and voltage settings produces a good quench and allows the secondary to ring properly, emitting a 750 kV discharge arc to the grounded electrode.

Then I remove the grounded electrode and allow the coil to discharge freely. It strikes the aluminized bubblewrap lining my observatory and grounds out… but this is a distance of 33 cm at least, which indicates that the coil is making on the order of a MegaVolt in this mode…. if you can believe spark gap tables.

This coil resonates at around 300 kHz or so. At the end of the video I’ve included a little slide show of some still photos of the coil discharging. The photos are all 30-second time exposures of multiple discharges.

The very last image makes a nice desktop image, and I’ve put the full size, full resolution version here for download if anyone is interested:


(Is this supposedly HD version really worth the five hours it takes to upload it? This clip is 600 MB, and I have a compressed version that is only about 100 MB. I’ll upload it later for comparison and reference.)

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